Directional couplers are passive devices used in RF communications to couple part of the transmission power in a first transmission line to a second transmission line. The coupling between the two transmission lines can be achieved by placing the two lines close to each other so that energy passing through the first line is coupled to the second line. With the increased drive for miniaturizing circuit components, conventional directional couplers can have small dimensions of both transmission lines. Even though such miniaturization can reduce the RF power loss in the main (first) transmission line, conventional miniaturized directional couplers are also characterized by very low directivity due to area limitation, which is undesirable in RF circuit design.